1. Field of the Invention
The present invention relates to a liquid processing apparatus and liquid processing method for planarizing a film on a substrate, such as a semiconductor wafer, by use of a process liquid.
2. Description of the Related Art
In general, in the process of manufacturing semiconductor devices, thin films, such as oxide films and nitride films, are formed as insulating films on the surface of a target substrate, such as a semiconductor wafer (which will be simply referred to as a wafer, hereinafter). As a method for forming a thin film, chemical vapor deposition (CVD) methods are utilized. In CVD methods, where a source gas is supplied from outside a wafer, as in a film formation process of the batch type performed in a vertical furnace, the thickness of a film thereby formed becomes larger at the peripheral portion of the wafer than at the central portion thereof, i.e., a concave shape (cone-shaped recess) is formed on the film. Further, where a film formation method other than CVD of the batch type is used, the thickness of a film thereby formed may become larger at the central portion, i.e., a convex shape (cone-shaped projection) may be formed on the film. Where contact holes are formed in a film having such a less uniform thickness, the diameter of the contact holes becomes smaller at a position with a film thickness larger than a predetermined value, while the diameter becomes larger at a position with a film thickness smaller than the predetermined value. If the diameters of the contact holes are different, a problem arises in that the product yield is decreased.
As a technique to solve this problem, U.S. Pat. No. 6,096,233 discloses the following technique. Specifically, at first, the thickness of a film, such as an oxide film, formed on a semiconductor wafer is detected at least at the peripheral and central portions of the film. Then, in accordance with detection signals, the film is planarized by supplying a process liquid (for example, hydrofluoric acid solution) that dissolves (etches) the film onto the wafer. At this time, the wafer is rotated, while a nozzle for supplying the process liquid is moved from the peripheral portion to the central portion of the wafer.
However, according to the technique disclosed in U.S. Pat. No. 6,096,233, liquid flicks occur at the peripheral portion of a wafer near a wafer chuck for holding the wafer. Consequently, a process liquid may be unevenly supplied onto the inner area of a film on the wafer, thereby deteriorating the uniformity of etching. Further, at the peripheral portion of the wafer near the wafer chuck, liquid supply is disturbed by the wafer chuck, thereby deteriorating the uniformity of etching, i.e., lowering the accuracy of the film thickness. In addition, since the process liquid is supplied while a nozzle for supplying the process liquid is moved for scanning, the process liquid consumption is large. Accordingly, it is also required to decrease the process liquid consumption.